Information Circular 6159: Method and Cost of Mining at Barr Mine, Tri-State Zinc and Lead District

United States Department of Commerce Bureau of Mines · 1929 · Historical

Above the ore in most parts of the mine is a firm, uniform limestone fron which the ore breaks free, leaving a fairly smcoth and even roof.

This 1929 document, Information Circular 6159: Method and Cost of Mining at Barr Mine, Tri-State Zinc and Lead District, is preserved in the Mountain Man Mining Library for research and reference. Original source: archive.org.

CircuLak 6159 Aucust, 1929

Information Circular

Department Of Commerce - Bureau Of Mines

Received

Sep 2 3 1929 0.3.U. Library

METHOD AND COST OF MINING AT BARR MINE, TRI-STATE ZINC AND LEAD DISTRICT

By

Oliver W. Keener

Circular No. 6159 August, 1929

Information Circular

Department Of Commerce - Bureau Of Mines

METHOD AND: COST OF MINING AT BARR MINE TRI-STATE ZINC AND LEAD DIstRiIcT 1

By Oliver W. Keener?

Introduction

The operation described herein differs from the usual practice in the Tri- State district in two important respects: (1) The ore is loaded into cars which are trammed to tne shaft and hoisted on self-dumping..cages, and (2) about 30 per cent of the ore is loaded by power.slovels. The four-month period covered by the cost data appended at the end of the paper immediately followed a period of about one year during which the mine was shut .down, and the expense incident to the resmption of operations is reflected in the costs. wa

The author acknowledges the assistance of C. F. Jackson, mining engineer, es Bureau of Mines, in the preparation of this paper and the compilation of the a. task a ee |

+. Ohtstory._.

The lease to the mine, which is located on a 60-acre tract, was acquired in September, 1916, and exploration by churn drilling was begun almost immediately alterward. The first shaft was sunk as the mill shaft in 1917, and production began in that year. Since the beginning of operations there have been several idle periods; the last resumption of 'operations was in January, 1929.

Geology And Ore Deposits

The ore bodies of this mine are located about the flanks of a huge lime dome. That section of the mine 'south of. No«. 2-shaft occurs in massive flint 150 feet thick, which has an overburden of Cherokee shale and Chester sand. The ore Minerals occur in brecciated zonés as "irregular-seams cementing fractures in the flint and as masses filling vugs and cavities. -The ore minerals consist of Sphalerite and some galena, associated with calcite and a highly silicious lime. rh massive structure about the Grdnd Falls chert horizon extends downward to the -foot level and was more or less mineralized throughout its entire mass. This

"as formerly mined on three levels in the richest horizons. The two upper levels te not being worked at present and are practically mined out.

Bae ee ne Ba ce ah ae

1 The Bureau of Mines will welcome reprinting of this article but requests that the following footnote acknowledgment be used: "Printed by permission of

the Director, U. S. Bureau of Mines. (Not subject to copyright.)"

a of the consulting engineers, U. S. Bureau of Mines.

Inf. Cir. 6159

The bottom of the ore now being mined lies at a depth of approximately 20 feet below the surface and rances in thiclness from 15 to 27 feet, averaging atc 45 feet. The ore is flat lying but has a slight dip to the north which carries the ore in the north section of the property to a depth of about 40 feet below th main shaft level, which ig at 300 feet. At this point the ore merges unconformadl with the Grand Falls chert without an appreciable line of demarkation.

In plan the ore bodies are very irregular, but are practically continuous for a distance of about 2,000 feet, measured in a curved line around the flanks 0 the dome. The width of the ore varies greatly, however, and in places splits int several channels or troughs with barren areas between them. In some places the ore is only 15 to 25 feet wide, while in others it attains widths of over 300 fee Figure 1 is a plan of the mine workings showing the stopes and extent of the ore bodies; Figure 2, A and B, shows cross sections of stopes in active areas.

Above the ore in most parts of the mine is a firm, uniform limestone fron which the ore breaks free, leaving a fairly smcoth and even roof. The system of fractures in which the ore bodies occur and which has governed the deposition of the ore passes into the roof as well, but is less pronounced there than in the or horizon itself.

Prospecting And Exploration

The 60-acre tract upon which this mine is located has been prospected by 205 churn-drill holes. The first drilling is laid out in rows of holes spaced at more or less regular intervals across the property and drilled primarily to locate the low spots in the structure where the ore is localized in this district. This drilling is followed by closer drilling where good ore or favorable conditi warrant.

No samples are taken after mining operations are started to determine th extent of the ore bodies. Estimates are made after a sufficient number of churn Grill holes are drilled into an ore eee to prove it up and prior to beginning mining operations.

The drill cuttings are carefully preserved and logged, and such samples as show as much as 1 per cent of ZnS and PbS are assayed. From a careful analys of these assays an ore body is blocked out. An estimate is then made of the tonnage available and the probable extraction. Experience has proved that these

estimates are lower than actual mill tests run.

Figure 3, shows a mumber of drill holes and an ore body sketched in. Th following is the method of ore estimation used:

Ore pillars, lower level ee Ore pillars, middle level YD

Ore pillars, upper level —

Upper level 0 ee me tee

Lower lv low"

Du OO WOM

0

'Scale in feet

Figure 1.— Plan of Barr mine

OUT JO SUOKLCS SARUS Ul SEOs jO SUOrIES s901D -—"Z AMS

«uVn~uVn BORSg "Y

> Ss _* — ** =

Figure 3.— Drill holes and ore body, projected:.on section at "A"—"A"

Inf. Cir. 6159 ' Average Assay Products (Assay, ft.) Hole No. Ore face Heiznt Zns eS _ 2us Pts 26 180-200 20 5.70 ae 114.00 -- 27 150-200 59 4.40 -- 220.00 -- 28 172-188 16 4.05 - a 64.80 -- 32 165-200 35 4.04 =e 141.40 -- 33 180-205 25 6.14 - - 153.50 -- 37 155-175 20 7.55 2.00 151.00 40.00 40 154-218 64 ?, 34 ae 469.76 -- 49 170-205 35. 3.91 -- 136.85 -- 50 165—205 40 10.40 ~ - 416.00 -- 1 1723-217 444 21.40 = 952.30 — 33 170-1873 273 15.30 1.02 420.75 28.05 Of 190—220 30 9.25 1.19 277.50 35-70 00 190~—200 10 2.14. 21.40 13)417 417(3539,26 103.75 32 8.49 0.25

$40.00 per ton Zn concentrates $90.00 per ton Pb concentrates used.

8.49 x 85 per cent extraction x $40.00 = $ 2.89 net 0.25 x 90 per cent extraction x $90.00 = 023

Less 8 per cent royalty 25 Mining and milling cost .. 1.60 — . 1.85 1.85 $ 1.27 net value per ton Area 17,040 x 32 ft ears e ~ cu. ft. per ton, tit Sunes Less 10 per cent pillars 4,194.5

37,750.5 net tonnage Net tonnage x 1.27 = $47,943.14, Value ore body.

Additional estimates are prepared from time to time as drilling progresses, e |

Early Mining Methods

2eading a on) Mining on the uvper levels was typical of the district. The t Ope system was used, and the ore was loaded into cans set on trucks; rans were hoisted to the surface, dumped, and immediately returned to wie Seas bottom horizon was'opened up cars were installed instead of about 36 d-loaded. Later mechanical shovels were introduced, and at. per cent of the ore. is mechanically loaded.

ec

Inf. Cir. 6159 | DEVELOPMENT SYSTEM

The mine is developed by a main overating shavt centrally located on the property and at the mill sits, and the lower ore horizon, which is tne ore now being mined, is developed from this shaft at the 300-foot level.. Development openings are carried in the'ore wherever possible, but several "pull drifts" are drive to reach isolated ore badies or to facilitate haulage between the active areas ant the shaft. |

There are two field shafts: on the property, one of which is equirped wits a double-deck cage for handling men and suppiizs and for ventilation. Tne otner shaft was used for working the upper horizon azd does not go down to the present level. | |

Development, as such, is very aifferert from that in most metal-mining districts in the United States, except for the pull drifts. Development headings in ore are carried wide and at the tov of the ore as a part of what in other districts would be stopirg. Where tne ore is not vver 40 ta 50 feet wide these headings are usually driven the full width of the ore, or the width between spotted pillars in wider ore bodies. The ore is stoped out between the reading and floor

of the level, keeping the stope face at an angle of about 45°.

The local rans of ore belov the main level are reached by snort inclines, and inclines are resorted to for minifig the ore in tne north section of tne mine which lies below the shaft level (fig. 2-B).

snafts.—- The mill shaft is 6 by 10 feet in the clear and has two compartments provided for hoisting self-dumping cages in balance. This shart is concreted from the collar to a depth of 10 feet and cribbed to the rock. Below this point the shaft is untimbered except for the necessary supports for the cage guid

The man shaft is a tvo compartment shaft 6 by 12 feet in the clear. One compartment is used for a double-deck man cage, and the other, which is housed ir 1s used as an airway and also contains a cage counterweight and pipeway and elec! conduits. <A force fan blows air down this compartment to the mine workings.

Pull Drifts.— Pull drifts are driven 7 by 7 feet to 8 by 10 feet and are untimbered. These drifts are usually driven on contract at an average price of $6 per foot. The contractor furnishes only the labor and explosives while the company furnishes all drilling equipment, air, and other supplies. The total co ranges from $10 to $12 per foot.

Figure 4, shows the drill round for pull drifts. Cut holes are drilled about 8 feet deep and all others about 7 feet, the usual round employing 4 cut holes, 2 relief holes, 3 roof holes, 3 "stope holes" (lifters), and 2 side holes or 14 holes in all. The holes are drilled with a medium-weight Leyner-type drif ing machine mounted on a 7-foot post or column and using 14-inch hollow round, lug-shank steel. The steel is made up in 2-foot changes with single 14° taper cross bits. The starters are made up with 2S-inch gauge and the changes with - 3/16 inch difference in gauge.

Figure 4.— Plan and profile of pull drift round. Circled numbers denote order of firing

Shaft round the same with the addition of two extra relief holes marked "xX"

Inf. Cir. 6159 :

Two men are employed on the' drill, usually on night shift, and the drift is mucked on the opposite shift, ordinarily bv one man. The average round is blasted with one box of 40 per cent gelatin powder using fuse and No. 8 caps for firing.

Present Mining Method

The ore is mined by driving a heading next the roof and about 7 feet in height. The heading is usually car:ied three. rounds or about 15 feet ahead of the stope which follows behind the heading. In low ore the stope is carried the full thickness of the ore. In high ore the stope is drilled and blasted with long flat stope holes at the bottom of the level as shown in Figure 5 with internediate rows of "splitter" holes as: required, depending upon the height of the stope. Stope and splitter holes are drilled up to a maximum of 18 fect in depth. The rows of holes are from 7 to 10 feet apart vertically with two or three holes about 10 feet apart in cach row, the number depending on the width of the stope. the stope holes (bottom row of holes) are drilled and blasted first, leaving a | vertical face from 7 to 10 feet high. 'The broken ore is only partly loaded out, enough being left against the face upon which to set up a tripod for drilling the splitter holes. Where. more than one row of splitter holes is required, the lower row is ss and blasted first, followed in order by the 'higher rows.

Figure 5, shows' the methods used for driving headings and of drilling and blasting the stope or bench. Headings are drilled from a post and other holes from a tripod: The holes are loaded vith 40 per cent ammonia powder aad blasted with fuse and No. 8 caps. "They are loaded to about two-thirds oF the distance from the bottom and no stemming is employed.

The width of the stope is limited by the er of pillars for support of the roof. This distance is usually about 30 feet but varies from 25 to 45 feet. for the average stope three holes in a row are thus required for breaking the Tound.

There are three two stage compressors, one of 888 cubic feet capacity and two of 401 cubic feet of free air per minute and with a working pressure of 100 bounds-per square inch at the compressor. The steel is handled in a round can and lowered and raised through a 16-inch borehole. The signal cord for the steel | hoistman is run through another borehole. _ an —_

The average number of tons of rock broken per machine shift during the period January 1 to Mav 1, 1929, was 64.2 tons. | |

Loading And Tramaing | 2

Two methods of loading are employed at this 'thine: "hand-loading into cars | and Power-shovel loading into cars. Hand-loading is done on contract, tne price ceing 38 to 415 cents per car of 14 tons each.' For hand-loading, 2<inch planks © ere laid before blasting down to provide a smooth floor from which to shovel. 'The average performance of hand muckers in this mine for the first four months of 1929 "as 24.9 tons per mucker shift.

Inf. Cir. 6159

There are two power shovels in the mine. These shovels are of the boon-and-dipper full-revolving type which move by caterpillar traction and are operated by a single 25 hp.'a.c. motor clutched to the swing hoist. and crowd mechanism. The dipper has a capacity of 10 'cubic feet, —

Cars are brought to the shovel on a single track branching into two tracks behind the shovel. 'Two cars at a time are spotted by mule haulage, and cars are spotted and loaded on alternate tracks.' The usual performance for the shovel is about 100 cars per shift, though as many as 116 cars or 175 cans have been loaded in four hours. The performance in mechanical, loading during the first four months of 1929 averaged 49 tons per man-shift. |

Haulage throughout the mine is by mules, of which there are eight in the mine at present. Mulés are shortly to be replaced by a 53-ton storage-battery locomotive on the main-line haulage. :

The track gauge is 24 inches' and 20-pound rails are used. The cars are equipped with roller bearings. | . (

There are three. 'inclines in the mine' over which cars are lowered and hoisted by small electrically driven hoists. | One slope is 300 feet long and the other about 30 feet long. The former' is on a 7 per cent grade and the latter is on a 45° slope. (Only oné car per trip is handled on' these inclines.

The cars are 'caged at the 'shaft bottom by. hand. There is a double track at each side of the shaft and a single runaround track around one end of the shaft. The loaded cars are run on from one side and bump the empties off the cage; the empty cars are 'released by a foot treadle operated by a man on the empt; car side. The oncoming loaded car strikés & latch which throws the cage stops into the stop position. again. bees

'PERCENTAGE oF EXTRACTION a

From 15 to 18 per cent of the area mined is left for pillars. The greate number of these are ore pillars and will eventually be mined. The leaner ones will be left. As the total height of the face is'more or less mineralized, there can be no precise factor determined as to the dilution of ore by waste. All rock

is run through the mill with no waste boulders discarded. This of course forces the richer ore bodies to furnish the bulk of the tonnage. 'The leaner areas furnish only that tonnage needed to keep the mill capacity 'avate critical efficient

: WAGE, CONTRACT AND BONUS: SYSTEM a

Labor is based on an eight-hour day. Muckers are paid from 38 to 414 cen per car according to the "layout" and: length of haul to the "lay—-by" or gathering track. This price fluctuates up or down with tne ore market, but is based on a price of $40 per ton of concentrates. _ For every $5: increase, shift wages are automatically increased 25 cents' per day and muckers * 1g cents per car. On a down ward market all Wages" are correspondingly decreased. This, however, is the gener practice throughout the district. The. average wage scale at this mine based on $40 per ton concentrates is as follows:

Inf. Cir. 6159

Machine operators ...... woe $ 4.75 TYOMUCTS .. 6d seresilkascewe eee 4.00 . Machine helpers .......... : 4.25 BLACKSMITHS 568060583660 5%% 6.00 Hoistmen ........ eS re 4.50 Powdermen ....c..seeee acess 5.00 Roof trimmers .......0.0.- ' 4.25 Hookers and cagers ........ 4.00 Shovel operators ...ceccsues 5.00 Tracumen ...... ee re eee , 4,50 VENTILATION |

The ventilation in the mine is by force draft supplied by a large fan at "0. 2 shaft. An individual motor-driven blower is sét.at the west portal of the long pull drift, which runs in a southeasterly direction, and air is supplied through 850 feet of galvanized sheet iron tubing of 16-inch diameter. Occasionally, a8 in raises, air is supplied through flexible tubing by small individual 2otor-driven blowers. Often churn-drill holes are equipped with blowers on the surface by which a eh of air: 'is forced into the workings.

| Fire Hazards

: As anne is no timbering in the workings, nor are there 'explosive Zases, che fire hazard is negligible. In case of fire at any of the surface plants, there are one or more means of egress through : GeEerent shasts or other properties, s0 that hes men are ) in little or. no danger. : . . |

'Safety Methods

The company madnteine a fulltime safety eae who makes reZular and systematic examinations of all workings and equipment and. is empowered to enforce ay safety measures he may deem necessary. An excellent spirit of cooperation exists between the men and the safety eerene so that. lost-time accidents are rare and minor accidents infrequent. me :

;

Inf. Cir. 6159

Barr mine.

Tons ore hoisted during period:

Tons ore hand-loaded:

Tons ore mechanically loaded:

Mining method:

| Under round Costs

Taele 1.— Summary Of Costs

Period covered:

Open stopes with pillar support.

January to April, 1929. |

er Ton of Ore Voisted

| Labcr__ Development@ -- Mining $.3101 Transportation? 21372 General under- , ground expense 0239 Surface expense (applicable to underground) 0315

Total

Supervision

Compressed!

air drills

and steel __ Powe $.0661

1 Includes power for compressing air. 2 No development in rock during period. 3 Includes mule and locomotive haulage, .

and hoisting.

~

Bs

Exvolosives

Otker supplies | Tots

Inf. Cir. 6159

Table 2.— Summary Of Costs In Units Of - Labor, Power, And Supplies

Rarr mine. Period covered: January to April, 1929. Tons ore hoisted during period: 45,344 Tons ore hand—-loaded: 33,506 fons ore mechanically loaded: 12,038

ining method: Open stopes with pillar support.

Man hours per ton

Breaking (drilling, blasting, and trimming) ......... 0223 Macking (hand and mechanical) ...cccccccccccccccececce 0279 Mucking (hand only) .....eecceccecees ee eee 321 Mucking (mechanical only) ..ce.cccccercececoessccons » 163 Haulage and hoisting .....ccccceseccececes setae raveeras ° 0305 Supervision w.ccccwcccvcreces decd. ena eae eee aise 2030 General ...cccvccccrccccscccsevcsscsccsvees pflecahe eleetans : ~O0ol Total man hours per ton underground .....-cecrereceee - 888 Average tons per man-shift underground ...-.eccccreeee 9.024 Average tons per man-shift surface labor .........e. 192.3 Labor, percentage of total cOSt ...-.-.eeeeeeeeevvees 55.5

3. Power and supplies per ton:

Explosives (lbs. per ton), 40 ner cent ammonia ...... . 805 Power: Air compression, kw.h. per ton ........-- 216 Hoisting, kw.h. per ton eoerecrcccocccces 2679

Ventilation, power loading, and haulage... 1.14 Total kw.h. per ton undergromnd .........-. ware 6.09 Other supplies in percentage of total power and supplies ........ eR oe ere ae ae cease 4760

Power, materials, and supplies, percentage of total underground cost ........... veer e ccoes 44.6

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